Can an amateur teach IELTS to students? I do not have proper knowledge of tenses, but I got 6.5 bands, and I am willing to work hard and become proficient.

No.Definitely not.

This test costs time energy and money so when you aim to attempt it go for some expert.

The nature of questions in all four sections is ver academic in nature so don't confuse it with just any other English Exam.One needs to be a master of strategies to help you understand the pattern, expected answers, tips to save time etc

Although in most of the institutes you will find tutors with similar band score only, I think it isn't ethical to play with anyone's future just for self improvement and some money.

If you know you aren't good at English grammar, then you must work on it first for at least 2 months, and then come to this profession with right intentions. It will only only assist your students, but also aid you in building a good reputation which is a prerequisite for a successful carrer in long run.

Of course, only an amateur teach IELTS. The professionals, with their 3 days Train the Trainer certificates will be mouthing only jargons. 

Best way to teahc IELTS or any other proficiency language test is o try and learn a language yourself, a language you are not very familiar or comfortable with. You will find the going gets easier as the process keeps getting harder.

I think its risk for students. If you really wanted to teach than first you should improve your english skills. It is not only beneficial for students but also for you. As in teaching field, first impress is consider as last impression. If students start feeling you dont posses requried skills than it would dent your personality and may be other students not able to put a trust on you. So, my advice would be, first join any group of teachers ( there are hundred of groups on FB) from which you can improve your english and than go with full force which is more impactfull.

An amateur can definitely teach. But, as some of the responses, it is not fair for the students who pay at the training institute to learn from an expert. Also, most of the institutes do hire amateurs as they can't afford experts.

Again, there is always an ideal ratio as to how much a student would be willing to pay to obtain training from an institute/trainer and the actual cost of expertise. It is not easy to tackle mature students who are good at English, specially who have studied at International Syllabus Schools. You would end up in a fix with such students in case you do guide them inappropriately.